The invention relates in general to the field of electro-optical and optoelectronic devices with vertical current injection electrodes and, in particular, to devices comprising micro-fabricated lasers (e.g., lateral electric field, vertical current injection lasers), optical detectors and semiconductor optical amplifiers involving a stack of III-V semiconductor gain materials.
For the monolithic integration of III-V optoelectronic devices (e.g., lasers, optical detectors, semiconductor optical amplifiers) on CMOS platforms, shallow III-V stacks are necessary, which are typically less than 500 nm thick. An optical mode typically exploited in such structures is a hybrid mode, meaning that the mode is partially in the III-V stack (where present) and partially in the waveguide underneath. The higher the overlap of the mode with the III-V active region (e.g., comprising multiple quantum wells), the easier the lasing is achieved. In such a configuration, however, one cannot use a simple top electrode covering the whole III-V region, as the large optical absorption caused by the metal electrode would prevent lasing action. A solution to this problem is to spatially separate the top electrode from the optical mode. For edge-emitting lasers, other lasers as used for hybrid configurations, e.g., a distributed Bragg reflector laser or a distributed feedback laser, wherein the mirrors are in the waveguide, this eventually leads to a configuration in which two top ohmic contacts and two bottom ohmic contacts are symmetrically positioned (as in FIG. 1). The current and hence the optical mode may, in such devices, be additionally confined by a current blocking layer.
However, as present inventors have realized, the resulting configuration leads to poor performance. Namely, such a configuration results in a very weak overlap between the gain profile (or recombination zone) and the fundamental mode position, which, in turn, impact the output power and the threshold currents.